Firearm cartridge

ABSTRACT

The firearm cartridge has an upper chamber adapted to house gunpowder and a bullet, a lower pocket adapted to house a primer, and a flash hole extending there between. The lower pocket has a ledge disposed generally perpendicularly to the flash hole. The flash hole is formed with a perimeter wall that has a convex curvature adjacent to the ledge of the primer pocket. The convex curvature of the flash hole perimeter wall can either be a continuous curve, or can be approximated by a series of smaller facets, as might be produced in various manufacturing processes.

RELATED APPLICATIONS

U.S. Provisional Patent Application No. 61/858,219 filed Jul. 25, 2013, and U.S. patent application Ser. No. 14/341,034 filed Jul. 25, 2015, are both hereby incorporated by reference herein as if fully set forth in their entirety.

FIELD OF THE INVENTION

The present invention relates to firearm cartridges, and more specifically to the flash hole design of a cartridge used in a modern firearm.

BACKGROUND OF THE INVENTION

An ammunition cartridge typically consists of a brass or steel case having a main chamber filled with a propellant such as smokeless powder and a bullet seated in the front of the case. A recessed pocket is provided in a rear face of the case to house a primer. At least one flash hole is provided in the wall separating the primer pocket from the chamber containing the propellant. When the primer is detonated, hot gas passes through the flash hole(s) and into the chamber to ignite the propellant. There are two styles of cartridges. A “Boxer” cartridge has one central flash hole approximately 0.060″ to 0.090″ in diameter and a primer pocket approximately 0.175″ in diameter. A “Berdan” cartridge has two diametrically opposing flash holes approximately 0.050″ in diameter.

In manufacturing, the flash hole is typically drilled or punched in the primer pocket from outside the cartridge towards the interior. This manufacturing operation occasionally results in a burr on the inside edge of the flash hole. Competitive shooters remove the burr with a special drill called “flash hole uniformer” to counter bore the flash hole from the inside of the cartridge.

As illustrated in FIG. 1, a conventional monolithic ammunition cartridge or ‘round’, generally designated 10, basically comprises a cup-shaped primer 12, a case 14, and a bullet 16. The primer contains a shock sensitive explosive 18. The case 14 is formed with an upper chamber 20 that contains a propellant such as smokeless gunpowder 22, a lower pocket 24 adapted to house the primer 12, and a relatively small diameter flash hole 26. The lower pocket 24 is typically defined by a cylindrical side wall 28 and an upper ledge 30 extending inwardly and generally perpendicularly to the side wall 28. The flash hole 26 is typically defined by a cylindrical perimeter wall 32 extending at a right angle from the upper ledge 30 of the primer pocket 24 to the upper chamber 20. When the primer 12 is struck by a firing pin (not shown), the primer explosive 18 is converted to ignition gas 34. The flash hole 26 enables the ignition gas 34 to flow from the primer pocket 24 to the powder chamber 20.

As illustrated in FIG. 2, the ignition gas 34 may experience flow resistance or back flow in the form of eddies or vortices 36 as it passes from the primer pocket 24 into the flash hole 26. It is believed that the sudden restriction imposed by the upper ledge 30 chokes the flow of the gas, thereby diminishing some of its force. It is further believed that if the flow of ignition gas through the flash hole were improved, the combustion of the powder 22 in the upper chamber of the cartridge and the subsequent travel of the bullet 16 would also be improved.

SUMMARY OF THE INVENTION

The present invention constitutes an improvement in a firearm cartridge. The cartridge may have a conventional upper chamber adapted to house gunpowder and a bullet, a lower pocket adapted to house a primer, and a flash hole extending there between. The lower pocket has a ledge disposed generally perpendicularly to the flash hole. The improvement comprises providing a flash hole that is formed with a perimeter wall having a generally convex curvature adjacent to the ledge of the primer pocket.

In order to create a generally convex curvature in the perimeter wall of the flash hole, various manufacturing techniques might be used, each resulting is subtle differences in the precise shape of the perimeter wall, though all resulting in the same general benefit described by this invention.

The simplest way to form a convex curvature in the flash hole perimeter wall is to use a drill with a concave profile at the tip. However, a generally convex curvature wall could also be formed by a lathe or mill, by cutting a profile which is stepped, such that a series of small discreet steps combine to create a generally convex form of the flash hole. Similarly, if a CNC lathe is used, such that tool movement is continuous while the part is turning, a generally convex curvature in the flash hole perimeter wall would be formed by a helical path of a scallop cut caused by the tool tip radius. Similarly, as chamfering is a common operation to remove a bur from a machined edge, a convex curvature of the flash hole perimeter wall could be approximated by creating a series of multiple chamfer cuts, each increasingly angled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a conventional firearm cartridge.

FIG. 2 is an enlarged fragmentary sectional view of the cartridge shown in FIG. 1, showing the patterns of gas flow and eddies as combustion gases from the primer flow into the cartridge main chamber.

FIG. 3 is a view similar to FIG. 2 and particularly illustrates a convex curve, 40, between the primer pocket and the flash hole perimeter wall.

FIG. 4 is an enlarged fragmentary sectional view of FIG. 3, illustrating an arc-shaped flash hole perimeter wall, 42.

FIG. 5 is a view similar to FIG. 4 and particularly illustrates a parabolic shaped flash hole perimeter wall, 43.

FIG. 6 is a view similar to FIGS. 4 and 5 and particularly illustrates an elliptical shaped flash hole perimeter wall, 44.

FIG. 7 is a sectional view, similar to FIG. 4, showing how the flash hole perimeter wall 26 can have an arc-shaped convex form 42, and compares how the arc shaped wall can be approximated by a series of steps, 27, and further compares how an increasingly fine set of steps, 28 can more closely match the generally convex shape, 42.

FIG. 8 is a sectional view, similar to FIG. 4, showing how the flash hole perimeter wall 26 can have an arc-shaped convex form 42, and compares how the arc shaped wall can be approximated by a series of scallop shaped cuts, 29, and further compares how an increasingly fine set of scallop shaped cuts, 31 can more closely match the generally convex shape, 42.

FIG. 9 is a sectional view, similar to FIG. 4, showing how the flash hole perimeter wall 26 can have an arc-shaped convex form 42, and compares how the arc shaped wall can be approximated by a series of increasingly steep chamfer cuts, 32.

FIG. 10 is a sectional view, similar to FIG. 4, showing how the flash hole perimeter wall 26 can have an arc-shaped convex form 42, and compares how the arc shaped wall can be approximated by a punching operation that allows the primer pocket separating wall to be swaged or drawn during the punching operation to closely match the generally convex shape, 42.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In incompressible flow (or gas flow at subsonic speeds of less than about Ma 0.7, where gas can effectively be modeled as incompressible), a constriction in pipe diameter will yield an increase in velocity, since mass flow rate along the pipe is theoretically constant. However, where there is compressible, or supersonic flow, as obtained from the detonation of a high explosive primer, a sudden constriction in a conduit will cause a choking condition or resistance that limits the flow of ignition gas through the constriction. It is believed that the amount of such resistance depends upon the shape of the constriction, particularly the inlet of the constriction. An opening entrance that is perpendicular to the axis of the conduit will cause a flow loss that is greater than the flow loss through a chamfered inlet which, in turn, will cause flow loss that is greater than a rounded inlet constriction. As these losses are examined in the context of supersonic flow of ignition gas in a firearm cartridge, the flash hole may be seen as a supersonic convergent nozzle, where the negative effect of the change from a large diameter to a small diameter on fluid flow may be mitigated by the shape of the constriction.

In order to allow the greatest and fastest flow of gas from the primer chamber to the powder chamber, it is therefore desired that the flash hole create the least amount of back pressure possible. To this end, it is proposed that the generally perpendicular intersection of the flash hole perimeter wall 32 and the primer pocket upper ledge 30 illustrated in FIG. 1 be eliminated in favor of, a less restrictive transition between the primer pocket and the flash hole. It is believed that a chamfer at the leading edge of the flash hole would act as a funnel for the primer gasses trying to pass through and ignite the powder. However, for supersonic flow, depending on the exact velocity, less obstruction would be provided by a generally curved entryway that becomes tangent to the through-hole, but does not make a full 90 degree ‘quarter round’ profile, perhaps making only a 45 or a 60 degree swing, creating something of a trumpet shape. A step better would be a flash hole entryway that is rounded with a circular profile on the primer side. As illustrated in FIG. 3, a flash hole perimeter wall 40 may be formed with a convex or rounded shape to streamline the ignition gas flow 34 and reduce flow resistance from the primer pocket 24 into the powder chamber 20.

Further, and depending on the gas parameters, other profiles which are not round might be utilized to advantage. Parabolic, elliptical, power series, Von Karmen, Haack, or many other shapes might be optimum. And again, any of these profiles might swing through a full 90 degrees, but might also only swing through a reduced angle. Further, any of these general profiles might be approximated by a series of smaller facets, including steps, or scallops, or progressive chamfers, or other finite steps as may be created depending on the cutting tool used to create the general profile. For instance, if the flash hole were cut on a CNC lathe using a cutter that had a small radius at the cutter tip, the general trumpet shaped profile of the flash hole would actually be made up of a series of overlapping scallops that followed a helical path to create the generally convex shape. Similarly, while the use of a single conical chamfer is known in the art to remove a bur or to soften a sharp edge, utilizing a series of two or more chamfers could create a series of ever steeper conic surfaces, such that the final profile approaches a trumpet shape, but is actually made up of multiple concentric conic surfaces.

As illustrated in FIG. 4, one of the possible profiles of the flash hole perimeter wall 26 may be a segment of a circle 42. The position and size of the arc 42 may be varied so that it is tangent to the flash hole at the inlet, and/or tangent to the flash hole at the outlet. FIG. 5 illustrates a flash hole perimeter wall that is a segment of a parabola 43. The parabolic segment maybe be tangent to the flash hole inlet and/or outlet. FIG. 6 illustrates a flash hole perimeter wall that is a segment of an ellipse 44. The elliptical segment profile may be tangent to the flash hole inlet and/or outlet.

FIG. 7 illustrates how a convex flash hole wall, 26, might have a circular arc shaped profile 42, however a generally similar profile can be approximated by a series of step shaped cuts, 27, and how a profile increasingly similar to the circular arc shaped profile, 42, can be achieved by using increasingly fine steps, 28.

FIG. 8 illustrates how a convex flash hole wall, 26, might have a circular arc shaped profile 42, however a generally similar profile can be approximated by a series of scallop shaped cuts, 29, and how a profile increasingly similar to the circular arc shaped profile, 42, can be achieved by using increasingly fine scallop shaped cuts, 31.

FIG. 9 illustrates how a convex flash hole wall, 26, might have a circular arc shaped profile 42, however a generally similar profile can be approximated by a series of concentric conic facets, 32.

FIG. 10 illustrates how a convex flash hole wall, 26, might have a circular arc shaped profile 42, however a generally similar profile can be created by a punching operation, such that the edge of the flash hole is drawn to a generally convex shape, 33.

Not shown, but illustrated in concept in previous illustrations cited above are the various curves which could be used to create curved transition shoulders or walls, including but not limited to circular arcs, elliptical arcs, parabolic arcs, power series arcs, Von Karmen profile or Haack profile arcs, or other mathematically defined curves.

It is contemplated that the foregoing convex perimeter wall of the flash hole may be formed with a drill, or end mill, or by a single point cutter in a lathe. The tip of the tool could have a concave curved surface which corresponds to any of the profiles described above, such that the drill can be used to drill or mill, or otherwise cut the various flash hole profiles into a cartridge or into a flash nipple. Alternatively, the convex perimeter wall of the flash hole could be formed by tools that have other tip shapes, however the tool position is controlled during the cutting process such that a series of many small cuts results in multiple facets along the perimeter wall for the flash hole, and whose blended shape is substantially convex. 

1-6. (canceled)
 7. A firearm cartridge case comprising: an upper chamber adapted to house gunpowder and a bullet, said upper chamber having a lower ledge, a lower pocket adapted to house a primer, said lower pocket having an upper ledge, and a flash hole extending between said upper chamber and said lower pocket and being defined by a perimeter wall, said flash hole perimeter wall having a convex curvature and extending from said lower ledge of said upper chamber to said upper ledge of said lower pocket, said flash hole having a lowermost diameter adjacent said upper ledge of said lower pocket and having an uppermost diameter adjacent said lower ledge of said upper chamber, wherein said lowermost diameter is larger than said uppermost diameter, and wherein a diameter of said flash hole between said lowermost and uppermost diameters only decreases from said lowermost diameter to said uppermost diameter, wherein the convex curvature of said perimeter wall is approximated through a plurality of shaped cuts.
 8. The firearm cartridge case of claim 7, wherein the convex curvature of said flash hole perimeter wall is a mathematically derived shape.
 9. The firearm cartridge case of claim 8, wherein the mathematically derived shape of said flash hole perimeter wall is selected from a group consisting of arcuate, parabolic, elliptical, Von Karmen, Haack, power series, and splined.
 10. The firearm cartridge case of claim 7, wherein said case is formed from a single, unitary, monolithic piece of metal.
 11. The firearm cartridge case of claim 10, wherein said metal is brass.
 12. The firearm cartridge case of claim 10, wherein said metal is steel.
 13. The firearm cartridge case of claim 7, wherein said lower ledge of said upper chamber is disposed generally perpendicularly to a longitudinal axis of said firearm cartridge case, and wherein said flash hole perimeter wall extends from a radially inner edge of said lower ledge of said upper chamber to said upper ledge of said lower pocket.
 14. The firearm cartridge case of claim 7, wherein said upper ledge of said lower pocket is disposed generally perpendicularly to a longitudinal axis of said firearm cartridge case, and wherein said flash hole perimeter wall extends from said lower ledge of said upper chamber to a radially inner edge of said upper ledge of said lower pocket.
 15. The firearm cartridge case of claim 7, wherein said lower ledge of said upper chamber is disposed generally perpendicularly to a longitudinal axis of said firearm cartridge case, wherein said upper ledge of said lower pocket is disposed generally perpendicularly to the longitudinal axis of said firearm cartridge case, and wherein said flash hole perimeter wall extends from a radially inner edge of said lower ledge of said upper chamber to a radially inner edge of said upper ledge of said lower pocket.
 16. The firearm cartridge case of claim 7 wherein said shaped cuts are step shaped cuts.
 17. The firearm cartridge case of claim 7 wherein said shaped cuts are scallop shaped cuts.
 18. The firearm cartridge case of claim 7 wherein said shaped cuts are concentric conic facets. 